Stabilizing means for radio receiving systems



July L0, 1928. 1,676,256

P. E. EDELMAN STABILIZING MEANS FOR RADIO RECEIVING SYSTEM Filed Nov. 17, 1924 2 Sheets-Sheet 1 IIII: 6 E

JAIL l l f lllll Ful y) 575536771420 July 10, 1928. Y 1,676,256

P. E. EDELMAN STABILIZING MEANS\FOR RADIO RECEIVING SYSTEM Filed Nov. 17, 1924 2 sheets-sheet 2 "Q 000mg R s,-

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*Ziuenig? Plug? Z. 526012600 Patented July 1 0, 1928.

PHILIP E. EDELMAN, OF CHICAGO, ILLINOIS.

STABILIZING- MEANS FOR- RADIO RECEIVING SYSTEMS.

, Application filed November 17, 1924. Serial No. 750,377.

Heretofore it has been customary in the art to introduce some additional stabilizing device, such as a potentiometer or other means to introduce losses in the circuits, to throttle out oscillation. In accordance with my present application, such external or extra stabilizing devices become unnecessary because in each instance the inductance in the plate circuit is proportioned with respect to the tuning in the grid circuit, so that the vacuum tube circuits are operated just below the point of undesired oscillation.)

The following illustrative drawingsshow the embodiment of this invention, in which- Fig. 1 is a diagrammatic drawing showing the electrical connections of a radio receiving set.

Fig. 2 is a diagrammatic drawing showing both the electrical and mechanical connections for a radio receiving set shown in.

Figure 1, whereby same maybe operated in accordance with this invention.

InFi 1, the antenna 1 is connected to coil 2 which connects tov ground 3 in the usual manner. The incoming .radio frequency energy is transferred from coil 2 to coil 4. A tuning condenser 5 tunes the 'd input circuit to the vacuum tube 14.- substantially similar tuned grid input circuit comprising the coil 6 and condenser 7 is arranged for the second vacuum tube 15. Another and substantially similar tuned grid input circuit is arranged for the vacuum tube 16 and comprises coil 8, condenser .9, with grid leak and condenser 17. Vacuum tube 16 serves as a detector tube, while tubes 1 1 and 15 serve as radio frequency amplifier stages. The plate circuit of the first tube 14 passes through a variablelinductance 10- which is coupled to coil v6 as shown. The plate circuit of vacuum tube 15 includes an adjustable inductance-11 which is coupled to coil 8, as shown. The inductance of both coils 10 and 11 can be simultaneously varied by means of the switch arms 13 when arranged and connected as shown in Fig. 2. The filaments of the vacuum tubes 14, 15, 16 and 18 receive current from battery 24. The tube 16 receives plate current from battery 25. The tubes 14, 15 and 18 receive plate current from batteries 25 and 26, as shown.' By-pass condenser 21 'is connected in the plate circuit of tube 16 in the customary manner. The by-pass condenser 20. is connected in the plate circuit of tube 18 in the customary manner. The plate circuit of tube 16 feeds output current through primary coil 22 of transformer 36. The secondary 23 of this transformer serves as a grid input circuit to vacuum tube 18. The plate output circuit of tube 18 passes through a loud speaker unit 19 in customary manner. Thus the detectorvacuum tube 16 has its output amplified via amplifier vacuum tube 18.

Fig; 1 thus shows two tuned radio stages,

a detectorand one audio stage of amplification. Rheostat 27 controls the filaments of the ampllficr tubes and rheostat 28 controls tlle operation current for the detector tube In the prior art, it has been found diflicult to control a tuned radio frequency circuit against undesired oscillation, and at the same time maintain uniform sensitivity in the circuit throughout the range of wave lengths for which the receiver is designed to operate. In some of the prior circuits, it has been customary to use a potentiometer or other device to throttle oscillation, or to use a capacity neutralized or similar circuit to balance out the tendency for the circuit to oscillate. Owing to the capacity between the grid, the plate.and the filament of the vacuum tube, the inductance connected in the plate circuit naturally tends to coact with the tuned grid circuit of the same tube, so

that oscillations occur. If, however, for a given wave length, the number of turns used in the plate circuit is reduced so that the plate circuit is untuned' and aperiodic so as to-have a very much lower natural frequency than the grid circuit, the tendency for undesirable oscillation can be avoided.

Now referring further to Fig. 1, the switch arms 13 simultaneously vary the two plate inductances 10 and 11. For example, the coil 10 and the coil 11 may be of similar construction wound with No.18 double cotton covered wire ona form 3" in diameter and tapped at 2, 4, 6, 8, 10, 12,14 and 16 turns. Thus'the first tap can connect in two turns in the plate circuit .for use at the lowest wave length. Then, continuing prohigher wave lengths until finally the sixteen turns are connected in the plate circuit for a wave length of say 550 meters.

The operation is as follows: The incoming energy is amplified in the first tube 14:, further amplified in the second tube circuit 15,

detected by vacuum tube 16 and passed through audio amplification, which is shown in this illustration by a single tube 18 in the customary manner. v

The coil 2 may comprise ten turns of No. 22 double cotton covered wire. The coil lmay comprise sixty-five turns of No. 22 double cotton covered wire, both coils 2 and t being wound on a tube 3" in diameter and coupled to each other. @oil 6 is constructed similarly to coil. 4. Coil 8 may have the arms 13 simultaneously. The taps 12 of the same dimensions as coil 4h. The tuning condensers 5, 7 and 9 may have a maximum capacity of .0005 m. f. Coil 10 is coupled to coil 6 and coil 11 is coupled to coil 8. The remainder of the circuit is substantially as is standard in the art in circuits of this character.

Referring now to Fig. .2, the movable plates of the condensers 7 and 9 and the switch arms 13 are simultaneously manipulated by means of a'connecting gear rack 31' coils l0 and 11 and the arrangement of the switch arms 13 is such that as the condenser 9 and the condenser 7 are increased in capacity by including more of the movable plates in the field of the fixed plates thereo the switch arms 13 connect in more of the turns of'the tap coils 10 and 11 simultaneously. This is the preferred arrangement though, as

Y .is obvious, the switch 13v might be separately manipulated by hand if desired. It is important to have the grid circuit tuned for any given wave length and simultaneously to have the plate circuit sufficiently detuned therefrom so that the vacuum tube circuits will not, oscillate undesirably for each given adjustment and this object may be accomplished with the apparatus connected in the circuits as just described.

In the prior art, it has been customary to do this by using a fixed plate coil as the primary of the tuned radio transformer with, for example, four or possibly six or seven turns of wire for the inductance, and this coil was designed so that'the tendency for oscillation would be overcome at the lowest wave length at which the receiver is to' be operated. When this is done, the radio transformer stages are clearly eflicient at this particular lowest wavelength range, but as the grid circuit is tuned to a higher wave length, the plate inductance coils being fixed,

become very inefficient and do not transfer the amplified radio frequency current evenapproximately nearly as well as at the lower wave lengths. Thus the receiver is an ineficient one when such fixed coils are used. llf, on the other hand, the inductances in the plate circuit which serve as the primary coils of the radio frequency transformers have their turns increased the amount of inductance in the plate circuit is proportioned to be of a value which will not cause undesired oscillation, when the grid circuit is tuned to one of the higher wave lengths, to which the receiver is responsive. As has been customary inthe prior art when the tuned grid circuit is operated at a lower wave length, this fixed plate inductance is I too large and will. cause undesired oscillation.

Various changes and modifications may be made within the scope of the claims and I have illustrated a practical working circuit by way of example only. Thus for example additional stages of tuned radio frequency may be added to the circuit in an exactly similar -manner by having additional plate and grid circuits arranged in the manner just described; also additional'audio circuits may be added without departing from the scope of this invention.

I claim:

1. In a radio receiver, a plurality of three element tubes for radio frequency amplification, said tubes having grid circuits and plate circuits, a tapped primary transformer coil included in each of said plate-circuits, a secondary transformer coil in eachof said grid circuits and interlinked with the primary coil of the preceding plate circuit, a variable condenser ineach of said grid circuits, and mechanically interconnected means for simultaneously varying the number of turns of said primary coilsin the plate circuits and var. 'ng said condensers for the purpose 'descri ed.

2. In a radio frequency amplifier circuit, a plurality of vacuum tubes having grid circuits and plate circuits connected in cascade,

a tapped primary transformer coil included in each of said plate circuits, a secondary transformer coil in each of said grid circuits and interlinked with the primary coil of the preceding circuit, means for simultaneously tunin each of said grid circuits, and means opera ly connected with said means for simultaneously varying the inductive coupling between said primary andsecondary coils in each stage to maintain a predetermined nonoscillating relation between the plate and grid circuits of each tube.

3. A radio amplifier having a series of transformer coupled stages with tuned secondaries included in the grid circuits thereof and adjustable primaries in the plate circuits thereof, means to simultaneously vary said primaries and changes in the tuning of said secondaries in relation to each other for efficient electromagnetic coupling without undesired feedback effects, a common control for tuning said grid circuits and correspondingly varying said electromagnetic couplings, the minimum setting of said electromagnetic coupling being proportioned at a. predetermined amount of the maximum setting thereof and progressively varied for each change of the tuning of said secondaries from minimum to maximum adjustment thereof.

4. In a radio circuit, a plurality of vacuum tubes, grid circuits and plate circuits connected thereto, connections therebetween in cooperative relation for preventing oscillations in said tubes, comprising means for simultaneously tuning the grid circuits of said tubes, means to vary the electrical values of said plate circuits, and means mechanically interconnected with said first means for adjusting said electrical values of said plate circuits simultaneously with the tuning of the corresponding grid circuits in a predetermined ratio between said means to vary the electrical values of said plate circuits and said means for tuning said grid circuits,

proportioned to control against the generation of oscillations in said circuits as the cuits operatively connected to said vacuum tubes, characterized by the fact that a common mechanical control means is provided therefor to simultaneously vary the operating values of said grid and said plate circuits in a predetermined ratio as said values are varied, proportioned to afford a high value of amplification via said vacuum tubes and circuits without permitting undesired oscillations as said operating values are varied, whereby for each range of adjustment of said grid circuits controlled by said mechanical control there is a corresponding adjusted operating value range for said plate circuits, with the electrical values of said plate circuits automatically increased by said mechanical control as said grid' circuits are adjusted for higher wave length ranges thereby, predetermined to be maintained by said mechanical control to control against the generation of undesired oscillations at each ad'ustment thereof.

Signed at Chicago this 12th day of November 1924.

PHILIP E. EDELMAN. 

